Patent Literature 1 describes a cell stack in which a cell frame, a positive electrode, a membrane, a negative electrode, and a cell frame are repeatedly stacked, and the resulting stack body is sandwiched between supply/drainage plates; and a redox flow battery including the cell stack. The cell frames each include a bipolar plate disposed between the positive electrode and the negative electrode, and a frame body that supports the bipolar plate from the outer periphery of the bipolar plate. In this configuration, a single cell is formed between the bipolar plates of adjacent cell frames.